The Epidemiology Branch (EBRP) is conducting a case-control study in Illinois and California to determine whether the use periconceptional vitamin supplements can reduce the risk of neural tube defects. Women having either a fetus or an infant with a neural tube defect in either state will be ascertained through perinatal networks, vital records, and other sources and will be matched to two controls on maternal race and geographic locale. One control will be a mother with a normal pregnancy, and the other the mother of an infant or fetus with a major health problem. Cases and controls will be interviewed within 3 months of the end of pregnancy to determine whether those having a conceptus with a neural tube defect are less likely to have used vitamins in the periconceptional period. The study design, personnel hiring, and forms development have now been completed and case identification is now underway. Field work has been contracted to the Department of Health, State of California and to Northwestern University in Illinois. To date approximately 225 cases and 400 control subjects have been identified and interviewed. Ascertainment of cases has been excellent in Illinois where the population is relatively small. Ascertainment has been good in California where, despite the fact that some cases are not identified, the total number of subjects obtained has been highly satisfactory.